This invention relates to an improved mold apparatus and method. In particular, the invention relates to an apparatus and method for creating designs on the interior of molds. Even more particularly, the invention relates to an apparatus and method for creating investment cast molds with complex designs on the interior and/or on the interior and exterior of the molds.
A tension arises when a business attempts to create objects with unique designs. The tension results from a conflict between various competing interests a business has. On one hand, businesses are interested in obtaining objects with unique designs that meet or exceed the customer""s requirements. On the other hand, the business must keep time and cost to a minimum in order to remain profitable. If time and money are no object, almost any object may be created with any unique designs imagined. Since time and money are always a concern, however, there is a practical limitation to the creation of objects with unique designs that results in the practical impossibility of creating some objects and some designs in a commercially reasonable, i.e. profitable, manner.
By way of example and not limitation, it is known throughout the munitions industry that certain types of notch patterns or grooves cut into the inside, and outside, walls of a projectile or warhead case dramatically improves their fragmentation characteristics, thereby increasing overall effectiveness. Typically, such notches are cut utilizing traditional machining methods such as broaching, shaping, milling and sawing.
A major drawback to these traditional machining methods is their inherent low production rate and high cost. The cost of the cutting tools, machinery, and labor required to implement these traditional machining methods can easily create a situation in which it is cost prohibitive or unprofitable to produce such items on a mass production basis. As a result, even though a number of warheads/projectiles in existence or currently in production do employ notches, they are very simple or less than optimal notch patterns. That is, currently straight-line configurations i.e. straight up-and-down notches or circumferential rings, are the only practical configurations for machined/broached projectile cases. Furthermore, while designs on the outside of the casing are easier, the preferred casing has designs on the inside or on the inside and outside in combination, which is, again , extraordinarily difficult to accomplish.
The prior art machined or broached warhead/projectile cases perform only adequately, because the fragments have a tendency to slab (not separate) due to the straight-line broaching/notching configuration limitation. As a result, fragmentation and, consequently, lethality is only modestly controlled and predictable when cases are created with the limited machine options known in the prior art.
Attempts have been made to create complex shapes without machining. Galliger, U.S. Pat. No. 6,019,927 discloses the use of a flexible and resilient positive pattern to make solid parts with complex geometry. However, the flexible and resilient pattern is simply used to create a hard shell into which metal is poured. That is, the Galliger device can only be used to create a solid thing and can not be used to create a casing with an interior with a complex geometry.
A further serious drawback of the prior art warhead/projectile case creation processes is that typically warhead/projectile cases are machined or forged from solid bar stock. Consequently, as much as seventy-five percent of the high-quality steel used to manufacture a warhead/projectile case goes into the scrap bin. This results in a huge waste of energy, time and material.
Still another serious drawback of the prior art techniques is that any hole, regardless of depth, that is machined in the solid bar stock, must have a zero draft angle (straight walls). A draft angle (taper), from the bottom of the hole to the beginning of the hole, creates a variation in wall thickness which is not acceptable in the munitions industry, for example. While complex, three dimensional, nonlinear designs can be created on the inside of cases with no draft angle, a myriad of specialized tooling and hardware is required which, for all practical purposes, makes the end product prohibitively expensive.
The investment casting process, also known as the xe2x80x9clost-wax xe2x80x9dcasting process, provides a viable solution to many of the problems associated with traditional machining methods. Despite an industry bias against cast casings, by its very nature, the investment casting process lends itself well to the creation of protruding or indented features, such as the aforementioned notches. Another advantage is the significant reduction in material waste as well as a reduction in the time required to perform any necessary finish machining operations, since parts may be cast to near-net shape.
The first step in the traditional investment casting process is to produce a wax replica of the part to be cast. This item is commonly referred to as a wax pattern or wax mold. Typically, wax patterns are produced by injecting melted wax into an aluminum mold assembly with internal cavities and/or cores conforming to the desired was pattern shape. Upon cooling and solidifying, the wax pattern must be removed from the aluminum assembly.
For the purposes of the present invention, this is where problems with the prior art arise. A hollow wax pattern with a round cross section, such as a wax pattern for producing the aforementioned warhead/projectile casing with an internal notch configuration, can not be produced by an aluminum mold of conventional design. That is because, in order to produce the hollow, notched interior surface, the mold design would have to incorporate an aluminum core, and, in addition this core would have to have protrusions in order to create indentations (notches) in the wax pattern. This creates an interference condition in which the removal of the wax pattern from the aluminum core is impossible without destroying the wax pattern.
Thus, there is a need in the art for an inexpensive apparatus and method for creating designs on the inside and outside of cases and other objects.
Accordingly, an apparatus for creating designs on the interior of molds includes a resilient form with an exterior and an interior, with a design formed on the exterior. A rigid support member is removably attached to the interior of the resilient form. A mold pattern, conformed to removably receive the rigid support member and the resilient form in combination, completes the basic assembly.
In one aspect of the invention, a passageway in the rigid support member is provided for introducing a gas between the rigid support member and the resilient form. In a further aspect of the invention, the design is a three dimensional design. In another aspect of the invention, a vacuum application device is provided for applying a vacuum to the resilient form. In a further aspect of the invention, the vacuum application device has a draft angle. In another aspect of the invention, the vacuum application device includes a plurality of extensions conformed to create a draft angle. In yet another aspect of the invention, the exterior of the resilient form has no draft angle and the interior has a draft angle. In another aspect of the invention, a lubricant is provided between the resilient form and the rigid support member.
In another embodiment of the invention, an apparatus for creating designs on the interior and exterior of a mold includes a first resilient form with an exterior and an interior, with a design on the interior. A rigid base is conformed to removably receive the exterior of the first resilient form. A second resilient form with an exterior and an interior, with a design on the exterior, is provided. A rigid support is removably attached to the interior of the second resilient form. The rigid base and the interior of the first resilient form is conformed to removably receive the rigid support member and the second resilient form in combination.
In another embodiment of the invention, in a process for creating an investment cast case, an apparatus for creating complex designs on the interior of the case includes a flexible sleeve with an exterior with a three dimensional design and no draft angle and an interior with a draft angle and a closed end and an open and. A support core, conformed to just receive and support the interior of the flexible sleeve from the closed end to the open end, is provided. Finally, a mold pattern is conformed to releasably receive the support core and flexible sleeve in combination.
In a further aspect of the invention, a passageway is provided in the support core conformed to introduce gas at the closed end of the flexible sleeve. In one aspect of the invention, a vacuum applicator is provided. In a further aspect of the invention, the interior has no draft angle. In another aspect of the invention, lubricant is provided between the flexible sleeve and the support core.
In another embodiment of the invention, in a process for creating investment cast cases, an apparatus for creating complex designs, including undercuts, notches, grooves, counter bores, slots, dimples and bosses, on the interior and exterior of a mold is provided.
In a further embodiment of the invention, a method of creating a design on the inside of a mold includes the steps of creating a resilient form with an exterior with a design and an interior. A rigid support member is attached to the interior of the resilient form. A mold pattern is created conformed to removably receive the resilient form and the rigid support member in combination. The resilient form and the rigid support member in combination are inserted into the mold pattern. Mold material is added to the mold pattern. Then the rigid support is removed. Finally, the resilient form is removed from the mold pattern.
In another aspect of the method, a passageway is provided in the rigid support member conformed to introduce gas between the rigid support member and the resilient form. Thereafter, gas is introduced in the passageway at the porper step to facilitate removal of the rigid support member. A further aspect of the method of this invention, includes forming the exterior with no draft angle and the interior with a draft angle. In another aspect of the method of the invention, a vacuum application device is provided and, after removing the rigid support from the old pattern, the vacuum application device is inserted within the interior of the resilient form in the mold pattern. Then, a vacuum is applied to the resilient form so as to collapse the resilient form around the vacuum application device and the vacuum application device is then removed from the mold pattern.
In still another aspect of the invention, the step of adding lubricant between the resilient form and the rigid support member is provided.
In another preferred embodiment a method of creating a design on the inside and the outside of a mold is provided.
In another preferred embodiment, a method for forming an investment cast case with a three dimensional design on the interior of the case includes the steps of creating a master pattern of the three-dimensional design in a female receiver. A male rigid support core is created with a draft angle, conformed to fit within the female receiver and including a passageway for introducing gas. The passageway is sealed with a removable pin so that the male rigid support core is a solid form. The male rigid support core is inserted into the female receiver and a flexible material forming fluid is introduced into the female receiver between the female receiver and the male rigid support core. The flexible material forming fluid is allowed to cure and create a flexible sleeve with a three dimensional design on the exterior and the interior conformed exactly to the male rigid support core. The removable pin is removed and compressed gas is blown into the passageway so that the gas is introduced between the rigid support core and the flexible sleeve. The flexible sleeve is removed from the master pattern female receiver. The male rigid support core is then inserted within the interior of the flexible sleeve and the flexible sleeve and rigid support core in combination are inserted within a mold pattern conformed to form the exterior of a case. Wax is added to the interior of the mold pattern and allowed to harden. The hardened wax and the combination of the flexible sleeve and the rigid support core are removed from the mold pattern. Compressed gas is blown into the passageway and the rigid support core is removed. The flexible sleeve is removed from the hardened wax. Finally, a case with three-dimensional designs on the inside of the case is created from the hardened wax by means of a lost wax process.
In a further aspect of the method of the invention, a vacuum applicator is provided and, after the rigid support core is removed from the hardened wax and the flexible sleeve, is inserted within the flexible sleeve. Then, a vacuum is applied to the inside of the flexible sleeve with the vacuum applicator so that the flexible sleeve is pulled away from the hardened wax and attached to the vacuum applicator. Then, the vacuum applicator, and flexible sleeve, is removed from the hardened wax. In another aspect of the invention, the vacuum applicator is formed with a draft angle.